A bottle cap including a top plate part which covers an opening of a bottle mouth, a cylindrical side wall part which vertically extends from a rim part of the top plate part and is screwed to the bottle mouth, and a plurality of projection parts that projects outside from the top plate part has been conventionally known. In such a bottle cap, an interval dimension between the projection parts is almost the same as the thickness of the side wall part (see, JP2012-500757A, for example).
When a conventional bottle cap is stacked on another bottle cap in an axis direction, an open end part of the side wall part is held between the projection parts formed in the top plate part of another bottle cap. These bottle caps are thereby connected. To connect bottle caps in which the axis lines thereof are not aligned, many projection parts are required. In accordance with an increase in the number of projection parts, higher manufacturing accuracy is required. The interval dimension between the projection parts is also required to be almost the same as the thickness of the side wall part. When the interval between the projection parts is narrow, it is difficult to clean up, for example, dust adhered between the projections.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a bottle cap capable of being connected to another bottle cap stacked in the axis direction with a simple configuration.